This is the Lord's Day

Q59 Which day of the seven hath God appointed to be the weekly sabbath?
From the beginning of the world to the resurrection of Christ, God appointed the seventh day of the week to be the weekly Sabbath; and the first day of the week ever since, to continue to the end of the world, which is the Christian Sabbath.

Q60 How is the sabbath to be sanctified?
The sabbath is to be sanctified by a holy resting all that day, even from such worldly employments and recreations as are lawful on other days; and spending the whole time in the public and private exercises of God's worship, except so much as is to be taken up in the works of necessity and mercy.